Resistors?

Kensai · 22nd February 2007, 01:10 PM

So, where can I source really big resistors? I'm looking for 23-25 ohms with a rating of at least 50watts.

Barring that, how would I go about wiring up multiple 8ohm 25 watt reisistors (the best I can find locally) to get what I need?

Kensai

EC8010 · 22nd February 2007, 01:41 PM

Vishay and Meggit do thick film non-inductive power resistors up to 300W (need a heatsink). In the values you need, wirewound will be inductive...

cc00541 · 22nd February 2007, 01:48 PM

Mouser is a good source for all things electrical. No minimum purchase as I recall as well.

The Vishay/Dale Heatsink cased resistors are probably what you want. Don't worry that they are wirewound. Their inductance will be in the microHenries.

C

http://www.mouser.com/search/Product...lkey71-RH50-24

EC8010 · 22nd February 2007, 02:12 PM

Quote:

Originally posted by cc00541
Their inductance will be in the microHenries.

Actually, you do have to worry about the inductance. I measured the power output of a single ended triode amplifier using a 8R Vishay wirewound aluminium-clad resistor as the dummy load and got more power than I expected at 1kHz. I also got a rising frequency response. This was because although it was 8R at DC, there was sufficient inductance at 1kHz, yes, 1kHz to allow the amplifier (which inevitably had a high output resistance) to deliver a slightly higher voltage across the load. When you then apply V²/R, the error is magnified.

Kensai · 22nd February 2007, 04:47 PM

Thanks for responses, guys.

What I'm looking to do is what Nelson Pass suggests by putting 23-25ohms in series with a Pioneer B20 to simulate the effects of a current source amp while using a voltage source one, which, if it works like he thinks it will (and so far, I've not seen anyone try it yet), should significantly increase bottom and top end output.

He actually put in a correction circuit to shelf down the top end a bit when driving the B20 which his test current source, so maybe this is the rising response you mention. The B20 is missing at least the top half octave, stock (more if listening off-axis at all), so this rising response won't be entirely bad, and I can actively EQ some out if there is too much.

On the other hand, I though that adding inductance would lowpass the driver, even if some unnoticeable amount. I'm thinking I'm way out of my league here, so thanks alot for chiming in here.

Kensai

Kensai · 22nd February 2007, 06:11 PM

How about something like the 25ohm 225watt ohmite listed on this page:

http://www.apexjr.com/miscellaneous.html

EC8010 · 22nd February 2007, 06:30 PM

Wirewound.

22nd February 2007, 01:10 PM	#1
Kensai diyAudio Member Join Date: Jan 2004 Location: St. Louis	reistors? So, where can I source really big resistors? I'm looking for 23-25 ohms with a rating of at least 50watts. Barring that, how would I go about wiring up multiple 8ohm 25 watt reisistors (the best I can find locally) to get what I need? Kensai

22nd February 2007, 01:41 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Vishay and Meggit do thick film non-inductive power resistors up to 300W (need a heatsink). In the values you need, wirewound will be inductive... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

22nd February 2007, 06:30 PM	#7
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Wirewound. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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22nd February 2007, 01:48 PM	#3
cc00541 diyAudio Member Join Date: Aug 2004 Location: latitude 40.8510 longitude -96.7592 altitude 362 meters	Mouser is a good source for all things electrical. No minimum purchase as I recall as well. The Vishay/Dale Heatsink cased resistors are probably what you want. Don't worry that they are wirewound. Their inductance will be in the microHenries. C http://www.mouser.com/search/Product...lkey71-RH50-24

22nd February 2007, 04:47 PM	#5
Kensai diyAudio Member Join Date: Jan 2004 Location: St. Louis	Thanks for responses, guys. What I'm looking to do is what Nelson Pass suggests by putting 23-25ohms in series with a Pioneer B20 to simulate the effects of a current source amp while using a voltage source one, which, if it works like he thinks it will (and so far, I've not seen anyone try it yet), should significantly increase bottom and top end output. He actually put in a correction circuit to shelf down the top end a bit when driving the B20 which his test current source, so maybe this is the rising response you mention. The B20 is missing at least the top half octave, stock (more if listening off-axis at all), so this rising response won't be entirely bad, and I can actively EQ some out if there is too much. On the other hand, I though that adding inductance would lowpass the driver, even if some unnoticeable amount. I'm thinking I'm way out of my league here, so thanks alot for chiming in here. Kensai

22nd February 2007, 06:11 PM	#6
Kensai diyAudio Member Join Date: Jan 2004 Location: St. Louis	How about something like the 25ohm 225watt ohmite listed on this page: http://www.apexjr.com/miscellaneous.html

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